1. Field of the Invention
The present invention relates to a method of and an apparatus for detecting control information necessary for controlling a drive unit. In particular, the present invention relates to a method of and an apparatus for detecting an angular velocity and a rotation angle of a rotating object rotated by a drive unit or a rotary shaft of the same.
2. Description of the Prior Art
Rotary encoders are in popular use as this type of detection apparatus in the art. FIG. 1 is a block diagram of a motor (drive unit) control system employing a rotary encoder. In FIG. 1, a rotary encoder 10 includes a disk 11 connected to a rotary shaft 1a of a motor 1 and photo interrupters 12 and 13 each comprising a light emitter and a light receiver. In the disk 11, a plurality of slits 14 are provided along the periphery of the disk 11 at predetermined intervals. The disk 11 also includes a slit 15, the slit 15 being nearer a center 11a of the disk 11 than the slits 14 are. The photo interrupter 12 is positioned so as to correspond to the slits 14, while the interrupter 13 to the slit 15. When one of the slits 14 and the photo interrupter 12 align, a ray from the emitter impinges through the slit 14 upon the receiver within the photo interrupter 12, hence turning on the photo interrupter 12. The photo interrupter 13 is turned on in the same manner. Thus, when the disk 11 is in rotation, the photo interrupters 12 and 13 generate pulse signals S.sub.12 and S.sub.13 correspondingly to the rotation speed of the disk 11.
The slits 14 and 15 are assigned different functions. The slit 15 is to detect a zero reference point, the zero reference point being defined as the rotation angle of the rotary shaft 1a when the slit 15 is in the position of the photo interrupter 13. On the other hand, the function of the slits 14 is to detect a rotation speed of the rotation shaft 1a and a relative angle to the zero reference point. In other words, information contained in the pulse signals S.sub.12 is about a rotation speed and a relative angle of the rotary shaft 1a, while information in the pulse signals S.sub.13 is about the zero reference point.
The pulse signals S.sub.12 and S.sub.13 are fed to a motor control circuit 3 which controls operation of the motor 1 according to its received control instructions, or designated values. The motor control circuit 3 calculates a rotation angle and the number of revolution of the rotary shaft 1a on the basis of the pulse signals S.sub.12 and S.sub.13, and then compares the calculated results with the control instructions and determines a control input for controlling the motor 1. Thus determined control input is then applied from the motor control circuit 3 to the motor 1 in order to maintain the motor 1 in an optimum appropriate operation.
In the rotary encoder 10, a rotation angle of the rotary shaft 1a is converted into a digital signal as explained above. Thus, the number of the slit have influence upon performance, resolution above all, of the rotary encoder 10. Although the rotary encoder 10, including the disk 11 in which a small number of the slits are provided, has poor performance, the performance thereof can be simply improved by providing more slits. However, there is a limit: naturally, the number of the slits cannot be endlessly increased. The rotary encoder 10 further has a problem that it is difficult to perform precise moment-by-moment detection of the rotary angle of the rotary shaft 1a. Therefore, the motor control circuit 3 cannot control the motor 1 on the basis of the digital signal from the rotary encoder 10.